1. Field of the Invention
The present invention relates to a dropout detecting apparatus for detecting a dropout of a reproduced signal in a signal reproducing apparatus such as a video tape recorder (VTR) and the like.
2. Description of the Prior Art
It is necessary for a VTR to correct for a dropout of a reproduced signal caused by a defect of the magnetic tape. Accordingly, to detect the dropout, dropout detecting apparatus have been used.
Conventional dropout detecting apparatus in extensive use are so constructed that they rectify and smooth the reproduced FM (frequency modulation) signal to obtain an envelope, and detect an amplitude of the envelope which is smaller than a predetermined level as being a dropout.
However, with this construction, when the time constant for smoothing is made small so as to detect a short time dropout, the envelope comes to include ripples to give rise to an erroneous detection; and when the time constant is increased so as to prevent the erroneous detection, the detection of the short time dropout becomes impossible.
On the other hand, in recent years, there has been a movement to perform the signal processing in a VTR, which had hitherto been analog processing, by digital processing so as to expect rationalization or high performance of the circuit. (For example, IEEE, Trans. on Consumer Electronics, vol CE-31, No.3, August 1985, pp 374-377, Japanese Laid-open Patent Application No.61-43083, etc.) Accordingly, it is desired for the dropout detection to be realized by digital signal processing and to be suited to a semiconductor system.